Specifications
XBee®/XBee‐PRO®SERFModules
©2009DigiInternational,Inc. 15
Serial Receive Buffer
When serial data enters the RF module through the DIN Pin (pin 3), the data is stored in the serial
receive buffer until it can be processed. Under certain conditions, the module may not be able to
process data in the serial receive buffer immediately. If large amounts of serial data are sent to
the module, CTS
flow control may be required to avoid overflowing the serial receive buffer.
Cases in which the serial receive buffer may become full and possibly overflow:
1. If the module is receiving a continuous stream of RF data, the data in the serial receive
buffer will not be transmitted until the module is no longer receiving RF data.
2. If the module is transmitting an RF data packet, the module may need to discover the desti-
nation address or establish a route to the destination. After transmitting the data, the module
may need to retransmit the data if an acknowledgment is not received, or if the transmission is
a broadcast. These issues could delay the processing of data in the serial receive buffer.
Serial Transmit Buffer
When RF data is received, the data is moved into the serial transmit buffer and sent out the UART.
If the serial transmit buffer becomes full enough such that all data in a received RF packet won’t fit
in the serial transmit buffer, the entire RF data packet is dropped.
Cases in which the serial transmit buffer may become full resulting in dropped RF
packets
1. If the RF data rate is set higher than the interface data rate of the module, the module
could receive data faster than it can send the data to the host.
2. If the host does not allow the module to transmit data out from the serial transmit buffer
because of being held off by hardware flow control.
Serial Flow Control
The CTS module pin is used to provide CTS flow control. CTS flow control provides an indication
to the host to stop sending serial data to the module. RTS flow control is not available. CTS
flow
control is always enabled.
When the serial receive buffer is 17 bytes away from being full, the module de-asserts CTS
(sets
it high) to signal to the host device to stop sending serial data. CTS
is re-asserted after the serial
receive buffer has 34 bytes of space.
The host device is expected to be able to receive data as fast as the Smart Energy RF Module
supplies it. Otherwise potentially critical data packets may be discarded.
Serial Interface Protocols
The Smart Energy RF Module only supports the API (Application Programming Interface) serial
interface.
API Operation
The frame-based API extends the level to which a host application can interact with the
networking capabilities of the module. When in API mode, all data entering and leaving the module
is contained in frames that define operations or events within the module.
Transmit Data Frames (received through the DIN pin (pin 3)) include:
• RF Transmit Data Frame
• Command Frame (equivalent to AT commands)
Receive Data Frames (sent out the DOUT pin (pin 2)) include:
• RF-received data frame
• Command response
• Event notifications such as reset, associate, disassociate, etc.
The API provides alternative means of configuring modules and routing data at the host
application layer. A host application can send data frames to the module that contain address and